Check out Microsoft's malicious software removal tool (Windows)

Nobody wants to think about getting a virus on his PC. On the good side, if you do, Microsoft provides a malicious software removal tool for detecting and removing specific viruses and worms. The tool works for Windows 7, Windows Vista, Windows XP, Windows 2000, and Windows Server 2003 and is updated regularly.

You can get the tool through Windows Update, in which case it runs and then deletes itself. You can run the tool anytime from the website www.microsoft.com/security/malwareremove/default.mspx.